Support apparatus with stress measuring capability

ABSTRACT

Apparatus for providing support to, and/or measuring the stress present in a potentially unstable structure, such as the roof of a coal or other underground mine, or a rock mass. The apparatus is an instrumented cable that has a center wire having a plurality of stress measuring devices attached along its length. Forming material is placed around the center wire and the stress measuring devices in order to provide protection and support. A plurality of noncenter wires extend generally longitudinally around the center wire, the stress measuring devices, and the forming material. Advantageously, the apparatus measures the stress placed thereon when inserted into the potentially unstable structure at more than one location along the length thereof, may be spun into a rock mass without damaging the stress measuring devices (or other components of the apparatus) and may be grouted into the potentially unstable structure with a variety of different grouts.

This Appln is a 371 of PCT/US99/04201 filed Feb. 25, 1999, which claimsbenefit of Provisional No. 60/076,138 filed Feb. 27, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to an apparatus for providing support toa potentially unstable structure, such as a rock mass or the roof of acoal or other underground mine, and/or for measuring the stress, strainand/or tension load placed on the apparatus when inserted into thepotentially unstable structure.

2. Background and Description of Related Art

Cables are strong wire ropes which are used in coal and other miningoperations in locations in which safe access may not be guaranteedduring mining to support the roof of the mine from the surface. Mostcables employed in mining operations are made by winding approximatelysix to eight small wire cables around a center wire cable, which iscalled a “kingwire.” Typical steel cables generally have a diameterranging between about 10 and 40 millimeters, generally have a lengthranging between about 5 and 50 meters, and are generally used inboreholes with a diameter between about 45 and 90 millimeters. Steelcables are installed in holes drilled or bored into the rock present inthe roof of the mine (boreholes, and bonded to the rock with grout, toreinforce the rock mass. The grout, which is usually a cement grout, acement mortar, or a chemical grout, is pumped into the borehole afterthe cable has been pushed into the borehole.

A large amount of stress is generally placed upon cables used forsupport in mining operations, and upon the cable bolts which are used tosecure these cables to the rock mass. The measuring of such stress onthe cables and cable bolts is important for risk management, so that therisk of partial or complete collapse of the roof of the mine, and theresulting injury or death to mine workers is minimized or preferablyeliminated.

“Stress” is an intangible quantity which cannot be measured directly. Itis only the manifestation of stress which is measured in, for example,pounds per square inch (psi), and is used to estimate the stress. Inmost mining and civil engineering applications, strain measuring devicesare installed in a borehole. “Strain” is the displacement of a cable asthe cable moves a linear distance (generally measured in microinches(10⁻³ inch)). “Tension” and “load” are the amount of force placed uponthe cable in, for example, pounds per foot (lbf), and may place a strainon the cable.

The monitoring of the roof support (by monitoring the stress placed onthe cables and cable bolts when inserted into the roof of a mine) hasbecome of increasing importance as deeper mines and higher productivityrequirements have led to more mechanization, and to larger excavations.This has resulted in increasing rates of mining-induced stress. As soonas an excavation has been made, the rock surrounding the excavationbegins to move and dilate into the new void. While the dilation cannotbe stopped, it can be controlled by measuring the amounts and directionsof stresses placed upon the cables and cable bolts inserted into therock. Because cables and cable bolts are a passive reinforcement systemin the rock mass, the load which is measured along the cable develops inresponse to deformation in the rock mass. Monitoring and warning deviceshave been developed to warn of relative movement between the rock massand support members for various support types.

Most of the devices for measuring stress or strain on cables and/orcable bolts inserted into unstable structures, such as those describedin U.S. Pat. Nos. 4,388,710, 4,803,888 and 5,284,107, are externaldevices which are positioned on the outside of the cables.

Hyett, “Development of a New Instrumented Cable Bolt to Monitor GroundSupport Loads in Underground Excavations,” 13th Mine Operators'Conference, Queen's University, Canada, Sudbury (1977), describes aninstrumented cable using Stretch Measurement to Access ReinforcementTension (SMART) technology. The SMART technology involves fabricating aminiature Multi-Point Borehole Extensometer (MPBX) within a temperedstainless steel tube which replaces the kingwire of a 7-wire strandcable. The displacement of six spring-loaded wires caused by stretch(elongation) of the cable occurs, and applied force or load is measured(in kN) using linear potentiometers, rather than strain gaugetechnology. Disadvantageously, and unlike the apparatus of the presentinvention, due to the fragility of the potentiometers, theseinstrumented cables cannot be spun into a rock mass without severelydamaging or destroying the potentiometers. Rather, the cables must behand-laid into the rock mass, which is time-consuming and laborintensive, and can only be used with concrete (cement) grout.

DeVries et al., “Optical Fiber Sensors for Monitoring Strain onRebar-Type and Cable-Type Bolts,” Proceedings of SPIE—The InternationalSociety For Optical Engineering 2446: 236-241 (1995), describes the useof short, gage-length optical fiber sensors (mirror and lightreflectivity sensors) which are surface mounted, using an epoxy resinadhesive, inside of a small groove of the kingwire of a 7-strand cable,for the measurement of relative strain in rebar-type and cable-typebolts used in the mining industry to support unstable material, or tokeep rock masses together. Disadvantageously, and unlike the apparatusof the present invention, the apparatus described by DeVries et al. onlymeasures strain at one location, rather than at more than one location,on the cable. Further, because optical fiber sensors are quite bulky, itis not possible to win a series of cables around a kingwire having theseoptical fiber sensors attached thereto.

There is a need for an improved apparatus for measuring the stressplaced upon a cable or other support inserted into an unstablestructure, such as the roof of a mine, which overcomes the difficultiesof the prior art.

The present invention provides an improved apparatus for providingsupport to an unstable structure, and for measuring the stress placedupon the apparatus, when inserted into the unstable structure todetermine whether or not the unstable structure is being subjected tomining-induced stress changes, or to stress changes caused by otherfactors. The apparatus of the invention measures the value of tension,strain and stress placed thereon at various locations along the lengthof the apparatus in, for example, areas of reduced clearance, such asboreholes present in a potentially unstable rock mass. The apparatusadvantageously measures stress placed thereon at more than one locationalong the length of the apparatus (at multiple locations), and issufficiently durable that it can be spun into a rock mass (or otherstructure) without damaging its components. Thus, the present inventionneed not be hand-laid. Further, the apparatus can be bonded into therock mass (or other structure) with a variety of different types ofgrout, such as cement-based grouts and resin-based grouts. Moreover,because stress measuring devices are present inside, rather than on theoutside, of the apparatus, the results produced by these stressmeasuring devices are less susceptible to environmental conditions,which can adversely affect resistance wire instruments. The apparatus ofthe invention may be quickly and efficiently installed into rock massesand other potentially unstable structures using routine procedures, andprovides a means for improving the reliability of roof support systemsin deep mine and other applications.

Additional advantages of the invention are set forth hereinbelow and areshown in the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for providing support to astructure, and for measuring stress placed on the apparatus when presentin the structure, said apparatus comprising:

(a) a center wire, the center wire having a length which is greater thenits width;

(b) a plurality of stress measuring devices, the stress measuringdevices being attached along the length of the center wire for measuringstress present on the apparatus;

(c) a forming material, the forming material being formed around thecenter wire and the stress measuring devices;

(d) a plurality of noncenter wires, each noncenter wire having a lengthwhich is greater than its width, and being wound around the length ofthe center wire, the stress measuring devices and the forming material;and

(e) a device for collecting data produced by the stress measuringdevices, the device being connected with the stress measuring devices;

wherein the stress placed on the apparatus can be measured at more thanone location along the length of the apparatus, and wherein theapparatus is spinnable into a rock mass without damaging the stressmeasuring devices.

The present invention also provides a method for supporting a structureand measuring strain within said structure, said method comprising:

(1) drilling a hole in said structure;

(2) placing an apparatus within said hole; and

(3) bonding said apparatus within said hole to said structure;

wherein said apparatus comprises:

(a) a center wire, said center wire having a length which is greaterthan its width;

(b) a plurality of stress measuring devices, said stress measuringdevices being attached along the length of said center wire formeasuring stress present on said apparatus;

(c) a forming material, said forming material being formed around saidcenter wire and said stress measuring devices;

(d) a plurality of noncenter wires, each noncenter wire having a lengthwhich is greater than its width, and being wound around the length ofsaid center wire, said stress measuring devices, and said formingmaterial; and

(e) a device for collecting data produced by said stress measuringdevices, said device being connected with said stress measuring devices;

wherein the stress placed on said apparatus can be measured at more thanone location along the length of said apparatus, and wherein saidapparatus is spinnable into a rock mass without damaging said stressmeasuring devices.

Additional features of the invention are set forth below, and are shownin the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows various components of the apparatus of the invention indifferent stages of production.

FIG. 1a shows a center wire having five stress measuring devicesattached thereto.

FIG. 1b shows the same center wire with forming material about to beplaced around the center wire.

FIG. 1c shows the same center wire with the forming material moldedaround the center wire and with a connecting device attached thereto.

FIG. 1d shows a perspective view of the completed apparatus.

FIG. 2 and FIG. 3 each show various components of the apparatus of theinvention.

FIG. 4 shows a wire strain gauge, having a resistor bonded with anelastic backing, for mounting on the center or kingwire.

FIG. 5 is a graph showing calibration data resulting from the experimentdescribed in the Example. Strand stress (from 0 to 35000 psi) on thehorizontal axes is plotted versus microstrain (from −2000 to 10,000microinches) on the vertical axis for the ten strain gauges described inthe Example. In FIG. 5, ♦ represents strain gauge number 1, ▪ representsstrain gauge number 2, ▴ represents strain gauge number 3, X representsstrain gauge number 4, ★ represents strain gauge number 5,  representsstrain gauge number 6, + represents strain gauge number 7, − representsstrain gauge number 8, - - represents strain gauge number 9, and represents strain gauge number 10.

FIG. 6 is a graph showing calibration data resulting from the experimentdescribed in the Example. Strand stress (from 0 to 35000 psi) on thehorizontal axis is plotted versus microstrain (from −2000 to 10,000microinches) on the vertical axis for the average sets of the five setsof two strain gauges described in the Example. In FIG. 6, ♦ representsaverage set number 1, ▪ represents average set number 2, ▴ representsaverage set number 3, X represents average set number 4 and ★ representsaverage set number 5.

FIG. 7 is a graph showing calibration data resulting from the experimentdescribed in the Example. Load (from 0 to 45000 lbf) placed upon theinstrumented cable on the horizontal axis is plotted versus microstrain(from −2000 to 10,000 microinches) on the vertical axis for the tenstrain gauges described in the Example. The symbols in FIG. 7 are thesame as described above for FIG. 5.

FIG. 8 is a graph showing calibration data resulting from the experimentdescribed in the Example. Load (from 0 to 45000 lbf) placed upon theinstrumented cable on the horizontal axis is plotted versus microstrain(from −2000 to 10,000 microinches) on the vertical axis for the averagesets of the five sets of two strain gauges described in the Example. Thesymbols in FIG. 8 are the same as described above for FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an apparatus for providing support to,and/or measuring the stress present in, an unstable structure. Bymeasuring the stress placed at more than one location along the lengthof the apparatus when inserted into a potentially unstable structure,the apparatus also measures the stress present in the structure and,thus, provides a warning of a potentially hazardous situation. Thepresent invention is not limited to the precise arrangements,configurations, dimensions, and/or instrumentalities shown in thedrawings, or described herein.

Preferred embodiments of the apparatus of the invention will now bedescribed with reference to the drawings. In the drawings, likereference symbols indicate the same parts of the apparatus throughoutthe different views thereof.

The apparatus illustrated in the accompanying figures generallycomprises an apparatus 10 for measuring the stress in an unstablestructure, such as a rock mass, the roof of a coal or other mine, aconcrete span for a bridge, a retaining wall near a highway, a railroador highway tunnel, a road cut, a trench, or a natural slope near aconstruction area, and for measuring the stress, strain, and/or tensionpresent along the length of the apparatus. The apparatus 10 can be usedto provide support to, and measure the stress present in, any structurein need of such support or stress measurement, many of which exist inthe construction industry.

The illustrated apparatus 10 comprises a center wire 12, a plurality ofstress measuring devices 14 attached along the length of the center wire12, a forming material 16 formed around the center wire 12 and thestress measuring devices 14, a plurality of noncenter wires 18 aroundthe length of the center wire 12, the stress measuring devices 14 andthe forming material 16, and a device for collecting data 20 produced bythe stress measuring devices 14.

The apparatus 10 generally has a diameter which ranges from about 0.4 toabout 2 inches, which preferably ranges from about 0.598 to about 0.602inches, with about 0.600 inches being most preferred. The apparatus 10has a length which generally ranges from about 1 to about 10,000 feet,which preferably ranges from about 3 to about 1,000 feet, and which morepreferably ranges from about 5 to about 100 feet, with about 10 to 25feet being most preferred. Of course, as those skilled in the art willrealize, dimensions larger or smaller than those give here (or elsewherein the specification) may be used, and even preferred, in particularapplications. The center wire 12 is preferably a strip of material whichfunctions as a kingwire in a cable, and which has a plurality of stressmeasuring devices 14 attached along the length of the strip, preferablyon both sides thereof. The center wire 12 generally has a length whichis greater than its width. The width of the center wire 12 willgenerally range from about 0.05 to about 0.5 inches, and preferablyranges from about 0.08975 to about 0.09775 inches, and more preferablyranges from about 0.09175 to about 0.09575 inches, with about 0.09375inches being most preferred. The length of the center wire 12 willgenerally be the same as the length of the apparatus 10, as is describedhereinabove. The thickness of the center wire 12 generally ranges fromabout 0.02725 to about 0.03525 inches, and preferably ranges from about0.02925 to about 0.03325 inches, with about 0.03123 to about 0.03125inches being most preferred.

The center wire 12 may be made from any material to which the stressmeasuring device 14 may be attached and, in conjunction with the formingmaterial 16 and plurality of noncenter wires 18 placed therearound, isdurable enough to withstand the loads which will be placed thereon. Forexample, the center wire 12 may be made from steel, with type 1020 coldroll steel being preferred.

A plurality of stress measuring devices 14 are attached along the lengthof the center wire 12, preferably with about one-half of the stressmeasuring devices 14 being attached along the length of one side of thecenter wire 12 and about one-half of the stress measuring device 14being attached along the length of the other side of the center wire 12.The number of stress measuring devices 14 which may be attached alongthe length of the center wire 12 will generally range from about 2 to1,000, will preferably range from about 3 to about 100, and will morepreferably range from about 4 to about 25, with about 10 to about 15being most preferred. The stress measuring devices 14 attached to thecenter wire 12 can be used to measure axial loads and bending loads(bending movements) due to strain differentials. It is preferable thatthe stress measuring devices 14 be spaced along the length of the centerwire 12 with from about 6 to about 60 inches of space between each ofthe stress measuring devices 14, according to the particularapplication, such as equally spaced apart. However, other arrangementsof the stress measuring devices 12 along the length of the center wire12 may also be use. It is also preferable that, for each stressmeasuring device 14 present on one side of the center wire 12, there isalso a corresponding stress measuring device 14 present directly acrossfrom the stress measuring device 14 on the other side of the center wire12, such that one half of the stress measuring devices 14 are present onone side of the center wire 12 and one half of the stress measuringdevices 14 are present on the other side of the center wire 12.

As used herein, the phrase “stress measuring device” means a devicewhich measures the amount of stress, strain and/or tension loaddeveloped along a cable (or similar device) placed into a structurewhich may be, or become, unstable, which is small enough to permitforming material and noncenter wires to be wound around it, which can bespun into a rock mass without being damaged, and still work properly(i.e., which need not be hand-laid into a rock mass), and which can beused with concrete- or cement-based grout and/or resin-based grout.These devices include wire or other strain gages made from variousmetals and alloys, and from cast polymide, glass epoxy, or phenolic orlaminated polymide. Such devices do not include potentiometers, whichcannot be spun into a rock mass without being significantly damaged ordestroyed, and/or optical fiber sensors, which are too large and bulkyto have forming material and noncenter wires around them. Unlike withmost of the known devices for measuring stress in an unstable structure,the stress measuring devices 14 employed in the apparatus 10 of theinvention are located inside of the apparatus and are internalcomponents of the apparatus. They can be installed into a rock mass orother structure without being damaged, and without needing anymodifications in resin grouts, for example, by spinning them with a roofbolting machine using cement-based grouts.

The stress measuring device 14 may be attached to the center wire 12 beany of several methods known in the art, such as by adhering themthereto with an epoxy resin adhesive or a ceramic cement. The stressmeasuring devices 14 measure the stress, strain or tension developedalong the length of the apparatus 10 when present in an unstablestructure, such as the roof of a coal or other mine, to determinewhether or not the apparatus 10 is being subjected to mining (or other)induced stress changes, for example, due to drilling operations. Thesestress measuring devices 14 measure the displacement of the apparatus 10in the unstable structure caused by the stretch of the apparatus 10which, in turn, is caused by a load being placed upon the apparatus 10.

One stress measuring device 14 which may be employed in the apparatus 10of the invention is a strain gauge, which is described in Froden,“Modern Instrumentation and Measurements in Physics & Engineering.” AIPHandbook of Modern Sensors; Physics, Designs and Applications (AmericanInstitute of Physics, New York, 1993), and which is commericallyavailable. A strain gauge is a resistive elastic sensor whose resistanceR is a function of applied strain (unit deformation). Because materialsresist deformation, force must be applied to cause deformation. Hence,resistance R can be related to applied force. That relationship isgenerally called the piezoresistive effect, and is expressed through thegauge factor S_(e) of the conductor as follows:${\frac{dR}{R} = {S_{e}e}},$

wherein dR is change in resistance and e is measured strain. For manymaterials, S_(e)≈2. For platinum, S_(e)≈6 and, as is indicatedhereinbelow, for platinum alloys. S_(e)≈4.0−6.0. For silicon, S_(e)≈−100to +150. In the experiments described in the Example, the gauge factoremployed was 2.095. For small variations in resistance not exceedingabout 2% (which is usually the case), the resistance R of a metallicwire is:

R=R_(o)(1+x)

where R_(o) is the resistance with no stress applied and x=S_(e)e. Forsemiconductive materials, the relationship depends on the dopingconcentration. Resistance decreases with compression and increases withtension. Characteristics of some resistance strain gauge are given inTable 1:

TABLE 1 Temperature Coefficients of gauge Resistivity, factor.resistance TCR(° C.⁻¹ · Material S_(e) Ω 10⁻⁶) Notes 57% Cu- 2.0 10010.8 S_(e) is constant over a wide 43% Ni range of strain. For use under260° C. Platinum 4.0-6.0 50 2160 For high temperature use. alloysSilicon −100 to 200 90,000 High sensitivity, +150 good for large strainmeasurements.

A wire strain gauge, which is illustrated in FIG. 4, is composed of aresistor 26 bonded with an elastic carrier (backing 28). The backing 28,in turn, is applied to the object where stress or force should bemeasured (i.e., the center wire 12 in the apparatus 10 of the presentinvention). Many metals can be used to fabricate strain gauges, andinclude the alloys constantan, nichrome, advance and karma.

The stress measuring devices 14 are connected with, and send data to, adevice for collecting data 20 by the stress measuring devices 14,preferably by a connecting device 22, which connects each of the stressmeasuring devices 14 with the device for collecting data 20. Theconnecting device 22 may, for example, be attached to the stressmeasuring device 14 using AWG30 wire, with two leads being attached toeach stress measuring device 14. The connecting device 22 is generallyconnected with the stress measuring devices 14 at a point in theassembly of the apparatus 10 of the invention prior to placing a formingmaterial 16 around the center wire 12 and stress measuring devices 14,such as prior to attaching the stress measuring devices 14 to the centerwire 12. The stress measuring devices 14 provide a readout of how theapparatus 10 is stretching, and displacements are recorded.

A 12-pin cannon plug, for example, may be employed to connect the stressmeasuring devices 14 to the device for collecting data 20. The 12-pincannon plug preferably has multiple wires attached to it, with two ofthese wires being attached to each stress measuring device 14 (oneattached to each side of the device 14), and with all of the wires beingattached to the device for collecting data 20. The 12-pin cannon plugmay be connected to a multiplexor, which sends voltage through thestress measuring devices 14 at a predetermined rate. The amount ofvoltage which may be sent generally ranges from about 15 to about 5000millivolts, and preferably ranges from about 15 to about 50 millivolts.The predetermined rate generally ranges from about 5 to about 5000millivolts, and preferably ranges from about 15 to about 5000millivolts. The voltage sent through the stress measuring devices 14decreases as the apparatus 10 is stretched, which occurs when a load isplaced thereon. The raw voltage data (voltage differential ormicrostrain voltage) is correlated with the amount of load being placedupon the apparatus 10 by, for example, balancing a 350 Ω Wheatstonebridge thereon.

Other devices which may be used to connect the stress measuring devices14 with the devices for collecting data 20 include Micro MeasurementsP3500, Campbell Scientific 21X, Omnidata-datalogger (CampbellScientific, Inc., Logan, Utah); other computer-based data collectiondevices may, of course, be used if desired.

The device for collecting data 20 may be any device which holds themeasurement value for viewing. For example, a datalogger system whichmay be connected to the stress measuring devices 14, and which reads andstores the data, is commercially available from Campbell Scientific,Inc.

The resulting center wire 12 having a plurality of stress measuringdevices 14 attached along the length thereof, is then formed into an“instrumented king wire” by placing a forming material 16 generallyaround the entire length of the resulting cable, so that the center wire12 and stress measuring devices 14 are preferably completely encasedwithin the forming material 16. Any forming material 16, such as epoxyor two-part liquid or other plastic mixes, may be used to form theinstrumented kingwire, with 1838 B epoxy being preferred.

A variety of different methods may be used to form the forming material16 around the center wire 12 having a plurality of stress measuringdevices 14 attached along the length thereof. For example, the centerwire 12 having the stress measuring devices 14 attached thereto may beplaced into an injection mold, and then the forming material 16, such asepoxy, may be injected into the mold, along the entire length of theinstrumented kingwire, thereby enclosing the center wire 12 and stressmeasuring devices 14 partially or completely within the forming material16. It is preferred that the center wire 12 and stress measuring devices14 be completely enclosed within the forming material 16.

The resulting epoxied or otherwise formed center wire 12 (instrumentedkingwire) is then wrapped with a plurality of noncenter wires 18, suchas steel wire ropes or steel stranded cables, preferably along theentire length thereof, and one at a time, by standard methods tostrengthen the epoxied instrumented kingwire and render the cable usablefor ground or other support, and for stress measurement. For example,each noncenter wire 18 may be hand or machine wrapped around the formedcenter wire 12, one at a time or more than one at a time.

The noncenter wires 18 may be the same or different, and may be anymaterial which, in conjunction with the epoxied instrumented kingwire,is durable enough to withstand the loads which may be placed thereonwhen present within an unstable structure. For example, the noncenterwires 18 may be made from various types of metals, such as steel, withgrade 270 K low relaxation steel being preferred. The noncenter wires 18will generally have a length width ranges from about 25 inches to about12,000 feet, and preferably ranges from about 33 inches to about 64feet, with about 32 feet being preferred. Because the noncenter wires 18are wrapped around the length of the epoxied instrumented kingwire,their length will generally be longer than the length of the center wire12. The diameter of the noncenter wires 18 generally ranges from about0.10 to about 0.75 inches, and preferably ranges from about 0.198 toabout 0.202 inches, and more preferably ranges from about 0.199 to about0.201 inches.

The number of noncenter wires 18 which may be wrapped around the epoxiedinstrumented center wire 12 generally ranges from about 1 to about10,000, preferably ranges from about 4 to about 1,000, and morepreferably ranges from about 5 to about 20, with about 6, 7, or 8, andpreferably 6, being most preferred.

The apparatus 10 of the invention will generally have a wedge coupling30 or like structure placed around the noncenter wires 18 on one end,and a hex barrel 32 or like structure placed around the wedge coupling30. The wedge coupling 30 and hex barrel 32 provide a structure on theoutside of the apparatus 10 of the invention which may be gripped by auser when the assembly is being inserted into a rock mass or otherunstable structure. The hex barrel 32 also functions to protect the12-pin cannon plug (or similar device), and to provide a structure to bewrenched by an insertion tool when the apparatus 10 is being insertedinto an unstable structure.

All of the materials and equipment used to make the apparatus of thepresent invention are commercially available from sources known to thoseof skill in the art. The apparatus of the invention may be madegenerally by cutting a commercially-available center wire having thedesired width and thickness with standard wire cutting tools to thedesired length. A plurality of commerically-available stress measuringdevices are then attached along the length of the center wire with, forexample, an epoxy resin. Preferably, the stress measuring devices arespaced apart equally, with each stress measuring device having acorresponding stress measuring device present on the opposite side ofthe center wire. A forming material, such as epoxy, is then placedaround the entire length of the center wire and attached stressmeasuring devices, for example, by standard injection moldingtechniques. The resulting instrumented formed kingwire is then wrappedalong the length thereof with a plurality of commercially-availablenoncenter wires having a desired thickness, which have been cut to thedesired length with standard wire cutting tools, preferably one at atime. Preferably, a wedge coupling 30 is placed around one end of theresulting instrumented cable, and a hex barrel is placed around thewedge coupling.

The resulting apparatus of the invention may then be quickly, easily andefficiently installed within an unstable structure, such as the roof ofa mine, to provide support thereto, and to measure the stress presenttherein, and formed along the length of the apparatus, with a drill, abolting machine, a spinning device, or by using other routine preceduresknown by those of skill in the art. The bolt head of the cable, which isformed by the wedge coupling 30 and hex barrel 32, may be used for theinsertion and storage of the 12-pin cannon plug, and as a nut to turnthe apparatus 10 once it is bonded into an unstable structure withgrout. Avantageously, the apparatus need not be hand-laid into thestructure, but may be spun into the structure by known methods.

For example, for use for support and strain measurement in a rock mass,an approximately 5-foot hole is drilled into the rock mass with routineequipment, and the apparatus is then spun into the hole (like a screw)by known methods, and embedded approximately 5-feet down in the rockmass (in a strained area of the rock mass) lengthwise. The apparatus isthen cemented into the rock mass by known methods with one of the groutsdescribed herein.

The apparatus of the invention advantageously may be bonded into a rockmass or other structure with a variety of different types of grouts,including cement-based grouts and resin-based grouts. Examples ofcement-based grouts which may be used include Portland cement andHydrastone. Examples of resin-based grouts which may be used includeepoxy resin, Fasloc (DU PONT, Hurricane, W. Va.) and Fasroc (Celtite,Grand Junction, Colo.).

Preferably, the grouting will be “full-length grouting,” with the entireapparatus being grouted into the rock mass or other structure to besupported. Generally, a hole which ranges from about 1 and ⅛ to about 1and ⅜ of an inch in diameter, and ranges from about 5 to about 16 feetin depth, is drilled into a rock mass, and the apparatus is fed intothis hole, and grouted therein in a desired position. Generally, onlythe head of the apparatus will protrude out of the rock mass. Theapparatus functions similarly to a beam in a house to glue the rock masstogether, and also to measure the strain developed along the length ofthe apparatus in the rock mass. Methods for the grouting of cables intoa rock mass or other structure are well-known by those of ordinary skillin the art.

Although certain preferred embodiments of the apparatus of the presentinvention have been shown and described herein, those or ordinary skillin the art will recognize numerous variations, modifications andsubstitutions which may be made as by adding, combining, subdividingparts, or by substituting equivalents. Thus, the invention is notlimited to the embodiments described herein.

All publications and patents cited throughout this document are herebyincorporated herein in their entireties by reference.

EXAMPLE

An instrumented cable was constructed and tested as described below. Theinstrumented cable had a steel kingwire measuring 60 inches in lengthand 0.20 inches in diameter, and had ten of the strain gauges shown inFIG. 4 (strain gauges numbers 1-10) attached along the length thereofwith an epoxy resin, with five strain gages placed on opposite sides ofthe kingwire, and with each of the five strain gauges evenly spacedapart by about 8 inches. Each strain gauge had a corresponding straingauge positioned at the same location on the kingwire, but on theopposite side of the kingwire, resulting in five sets of strain gaugesformed from ten separate strain gauges. The resulting instrumentedkingwire was attached to a 12-pin cannon plug which, in turn, wasconnected with a datalogger system for collecting data produced by thestress measuring devices. The instrumented kingwire was then placed intoan injection mold, and epoxy (3M 1838 B epoxy) was injected into themold along the entire length of the kingwire. The resulting epoxiedkingwire was then wrapped with six steel cables (one at a time)measuring 60 inches in length and 0.60 inches in diameter by standardmethods along the entire length thereof.

A series of calibration tests was performed on the resultinginstrumented cable. The results of these calibration tests are showngraphically in FIGS. 5-8. These results show that the instrumented cablefunctioned properly to measure the strain (in microinches) presentthereon at different levels of stress (in psi) or load (in lbf). Datarepresenting momental strain was collected for each of the ten separatestrain gauges (gauges 1-10 in FIGS. 5 and 7), and then the averagebetween each of the five sets of the ten strain gauges (one on each sideof the kingwire) was determined in order to show the true axial strainpresent on the instrumented cable (average sets 1-5 in FIGS. 6 and 8),rather than a momental strain. The calibration tests for the averagesets of strain gauges were performed using the data collected from thefollowing strain gauges:

Average Set Strain Gauges 1 1 and 6 2 2 and 7 3 3 and 8 4 4 and 9 5  5and 10

The following equations were employed to determine theload-stress-strain relationships: $\begin{matrix}{\begin{matrix}{microstrain} \\({microinches})\end{matrix} = \frac{{length}\quad {of}\quad {cable}\quad ({microinches})}{{change}\quad {in}\quad {length}\quad {of}\quad {cable}\quad ({microinches})}} \\{\begin{matrix}{{strand}\quad {stress}} \\({psi})\end{matrix} = \frac{{load}\quad ( {{pounds}\quad {per}\quad {foot}} )}{{area}\quad {of}\quad {the}\quad {cable}\quad ({microinches})}}\end{matrix}$

The results of these calibration tests are shown in FIGS. 6 and 8.

What is claimed is:
 1. An apparatus for providing support to astructure, and for measuring stress placed upon said apparatus whenpresent in said structure, said apparatus comprising: (a) an elongatecenter wire having a length which is greater than its width; (b) aplurality of stress measuring devices, said stress measuring devicesbeing attached along said length of said center wire for measuringstress present on said apparatus; (c) a forming material, said formingmaterial being formed around said center wire and said stress measuringdevices; (d) a plurality of noncenter wires, each noncenter wire havinga length which is greater than its width, extending generallylongitudinally of said center wire and being wound around the length ofsaid center wire, said stress measuring devices, and said formingmaterial; and (e) a device for collecting data produced by said stressmeasuring devices, said device being connected with said stressmeasuring devices; wherein the stress placed on said apparatus ismeasured at more than one location along the length of said apparatus,and wherein said apparatus is spinnable into a rock mass withoutdamaging said stress measuring devices.
 2. The apparatus of claim 1wherein said apparatus is configured to be bonded to said structure witheither concrete-based or resin-based grouts.
 3. The apparatus of claim1, wherein said apparatus has a diameter which ranges from about 0.4 toabout 2 inches, and a length which ranges from about 1 to about 10,000feet.
 4. The apparatus of claim 1, wherein said center wire is made fromsteel.
 5. The apparatus of claim 4, wherein said noncenter wires aremade from steel.
 6. The apparatus of claim 1, wherein from about 2 toabout 1,000 of said stress measuring devices are attached to said centerwire.
 7. The apparatus of claim 1, wherein said forming material isepoxy.
 8. The apparatus of claim 1, wherein from about 1 to 10,000 ofsaid noncenter wires are wound around said center wire, said stressmeasuring devices and said forming material.
 9. The apparatus of claim8, wherein the diameter of said apparatus ranges from about 0.598 toabout 0.602 inches, and the length of said apparatus ranges from about 3to about 1,000 feet.
 10. The apparatus of claim 1, wherein from about 4to about 1,000 of said noncenter wires are wound around said centerwire, said stress measuring devices, and said forming material.
 11. Theapparatus of claim 10, wherein from about 3 to about 100 of said stressmeasuring devices are attached to said center wire.
 12. The apparatus ofclaim 11, wherein the length of said apparatus ranges from about 5 toabout 100 feet.
 13. The apparatus of claim 1, wherein from about 5 toabout 20 of said noncenter wires are wound around said center wire, saidstress measuring devices, and said forming material.
 14. The apparatusof claim 1, wherein said center wire is made of type 1020 cold rollsteel.
 15. The apparatus of claim 14, wherein said noncenter wires aremade from grade 270K low relaxation steel.
 16. The apparatus of claim 1,wherein said stress measuring devices are strain gauges.
 17. Theapparatus of claim 1, wherein said forming material is 1838 B epoxy. 18.The apparatus of claim 17, wherein said noncenter wires are steel wireropes or steel stranded cables.
 19. The apparatus of claim 18, whereinfrom about 4 to about 25 of said stress measuring devices are attachedto said center wire.
 20. The apparatus of claim 19, wherein said stressmeasuring devices are attached to said center wire with an epoxy resinadhesive.
 21. The apparatus of claim 20, wherein from about 6 to about 8of said noncenter wires are wrapped around said center wire, said stressmeasuring devices, and said forming material.
 22. The apparatus of claim1, wherein about one half of said stress measuring devices are aboutequally spaced apart from each other on one side of said center wire,and about the other one half of said stress measuring devices are aboutequally spaced apart from each other on the other side of said centerwire.
 23. The apparatus of claim 1, wherein said stress measuringdevices are connected with said device for collecting data by aconnecting device.
 24. The apparatus of claim 23, wherein saidconnecting device is a 12-pin cannon plug attached to a multiplexor, andwherein said multiplexor sends voltage through said stress measuringdevices at a predetermined rate.
 25. The apparatus of claim 24, whereinsaid device for collecting data is a datalogger system.
 26. Theapparatus of claim 23 wherein said stress measuring devices are wirestrain gauges.
 27. The apparatus of claim 26, wherein the length of saidapparatus is about 16 feet.
 28. The apparatus of claim 27, wherein about6 of said noncenter wires are wound around said center wire, said stressmeasuring devices and said forming material.
 29. The apparatus of claim28, wherein said voltage ranges from about 15 to about 5000 millivolts.30. The apparatus of claim 2, wherein said grouts are Portland Cement,epoxy resin, Fasloc or Fasroc.
 31. The apparatus of claim 1, whichadditionally comprises a wedge coupling placed around one end of theapparatus, and a hex barrel placed around the wedge coupling.
 32. Amethod of supporting a structure and measuring strain within saidstructure, said method comprising: (1) drilling a hole in saidstructure; (2) placing an apparatus within said hole; and (3) bondingsaid apparatus within said hole to said structure; wherein saidapparatus comprises: (a) an elongate center wire having a length whichis greater than its width; (b) a plurality of stress measuring devices,said stress measuring devices being attached along the length of saidcenter wire for measuring stress present on said apparatus; (c) aforming material, said forming material being formed around said centerwire and said stress measuring devices; (d) a plurality of elongatenoncenter wires, each noncenter wire having a length width is greaterthan its width, extending generally longitudinally of said center wireand being wound around the length of said center wire, said stressmeasuring devices, and said forming material; and (e) a device forcollecting data produced by said stress measuring devices, said devicebeing connected with said stress measuring devices; wherein the stressplaced on said apparatus is measured at more than one location along thelength of said apparatus, and wherein said apparatus is spinnable into arock mass without damaging said stress measuring devices.
 33. Theapparatus of claim 1, wherein said center wire has a first substantiallyflat side and said stress measuring devices comprise strain gagessecured to said first flat side.
 34. The apparatus of claim 33, whereinsaid center wire has a second substantially flat side and said straingauges are secured to each of said flat sides.
 35. The apparatus ofclaim 34, wherein said forming material comprises two forming membersdisposed on opposite sides of said center wire, each having asubstantially flat surface facing said center wire, with the center andthe plurality of stress measuring devices being sandwiched between thetwo forming members.
 36. The apparatus of claim 35, wherein each of thetwo forming members has a substantially semi-cylindrical configuration.37. The apparatus of claim 1 further including a wedge coupling coveringan end of the noncenter wires, the wedge coupling aiding in grasping theapparatus.